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Lunar and Solar Eclipses

This illustration shows the Moon passing through Earth's shadow during a typical lunar eclipse. The Moon is slightly tinted when it passes through the light outer portion of the shadow, the penumbra, but turns dark red as it passes through the central portion of the shadow, called the umbra. [Tim Jones]An eclipse is the result of the total or partial masking of a celestial body by another along an observer's line of sight. Solar eclipses result from the Moon blocking the Sun relative to the Earth; thus Earth, Moon and Sun all lie on a line. Lunar eclipses work the same way in a different order: Moon, Earth and Sun all on a line. In this case the Earth's shadow hides the Moon from view.

When are this year's solar and lunar eclipses?

January 31: As seen from most of the United States, the Moon will appear dark orange or red as it undergoes a total eclipse, passing through Earth's dark shadow.

July 12: A partial solar eclipse will be visible across the Southern Ocean between Australia and Antarctica.

July 27: A total lunar eclipse will be visible across much of the eastern hemisphere and parts of South America, but not North America.

August 11: A partial solar eclipse will be visible across Europe and most of Asia and Africa, but not the Americas.

What is the difference between a lunar and a solar eclipse?

From our perspective on Earth, two types of eclipses occur: lunar, the blocking of the Moon by Earth's shadow, and solar, the obstruction of the Sun by the Moon.

When the Moon passes between Sun and Earth, the lunar shadow is seen as a solar eclipse on Earth. When Earth passes directly between Sun and Moon, its shadow creates a lunar eclipse.

Lunar eclipses can only happen when the Moon is opposite the Sun in the sky, a monthly occurrence we know as a full Moon. But lunar eclipses do not occur every month because the Moon's orbit is tilted five degrees from Earth's orbit around the Sun. Without the tilt, lunar eclipses would occur every month.

Lunar and solar eclipses occur with about equal frequency. Lunar eclipses are more widely visible because Earth casts a much larger shadow on the Moon during a lunar eclipse than the Moon casts on Earth during a solar eclipse. As a result, you are more likely to see a lunar eclipse than a solar eclipse.

The Moon casts its shadow on Earth's surface during a total solar eclipse. [Tim Jones]

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